1. Field
The present invention relates to multicast communications, in a wireline or a wireless communication system. More particularly, the present invention relates to a system and method for a multicast service initiation in such a communication system.
2. Background
Communication systems have been developed to allow transmission of information signals from an origination station to a physically distinct destination station. In transmitting an information signal from the origination station over a communication channel, the information signal is first converted into a form suitable for efficient transmission over the communication channel. Conversion, or modulation, of the information signal involves varying a parameter of a carrier wave in accordance with the information signal in such a way that the spectrum of the resulting modulated carrier wave is confined within the communication channel bandwidth. At the destination station, the original information signal is reconstructed from the modulated carrier wave received over the communication channel. In general, such a reconstruction is achieved by using an inverse of the modulation process employed by the origination station.
Modulation also facilitates multiple-access, i.e., simultaneous transmission and/or reception, of several signals over a common communication channel. Multiple-access communication systems often include a plurality of remote subscriber units requiring intermittent access of relatively short duration rather than continuous access to the common communication channel. Several multiple-access techniques are known in the art, such as time division multiple-access (TDMA), and frequency division multiple-access (FDMA). Another type of a multiple-access technique is a code division multiple-access (CDMA) spread spectrum system that conforms to the “TIA/EIA/IS-95 Mobile Station-Base Station Compatibility Standard for Dual-Mode Wide-Band Spread Spectrum Cellular System,” hereinafter referred to as the IS-95 standard. The use of CDMA techniques in a multiple-access communication system is disclosed in U.S. Pat. No. 4,901,307, entitled “SPREAD SPECTRUM MULTIPLE-ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS,” and U.S. Pat. No. 5,103,459, entitled “SYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM,” both assigned to the assignee of the present invention.
A multiple-access communication system may be a wireless or wire-line and may carry voice traffic and/or data traffic. An example of a communication system carrying both voice and data traffic is a system in accordance with the IS-95 standard, which specifies transmitting voice and data traffic over the communication channel. A method for transmitting data in code channel frames of fixed size is described in detail in U.S. Pat. No. 5,504,773, entitled “METHOD AND APPARATUS FOR THE FORMATTING OF DATA FOR TRANSMISSION”, assigned to the assignee of the present invention. In accordance with the IS-95 standard, the data traffic or voice traffic is partitioned into code channel frames that are 20 milliseconds wide with data rates as high as 14.4 Kbps. Additional examples of communication systems carrying both voice and data traffic comprise communication systems conforming to the “3rd Generation Partnership Project” (3GPP), embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), or “TR-45.5 Physical Layer Standard for cdma2000 Spread Spectrum Systems” (the IS-2000 standard).
In a multiple-access wireless communication system, communications between users are conducted through one or more base stations. The term user refers to both animate and inanimate entities. A first user on one wireless subscriber station communicates to a second user on a second wireless subscriber station by conveying information signal on a reverse link to a base station. The base station receives the information signal and conveys the information signal on a forward link to the second subscriber station. If the second subscriber station is not in the area served by the base station, the base station routs the data to another base station, in whose service area the area the second subscriber station is. The second base station then conveys the information signal on a forward link to the second subscriber station. The forward link refers to transmission from a base station to a wireless subscriber station and the reverse link refers to transmission from a wireless subscriber station to a base station. Likewise, the communication can be conducted between a first user on a wireless subscriber station and a second user on a landline station. A base station receives the data from the first user on the wireless subscriber station on a reverse link, and routes the data through a public switched telephone network (PSTN) to the second user on a landline station. In many communication systems, e.g., IS-95, W-CDMA, IS-2000, the forward link and the reverse link are allocated separate frequencies.
The above described wireless communication system is an example of a point-to-point service, where information from the first user is intended for the second user only. In contrast, a multicast service is a service where the information provided by a source, a user or a content server, is intended for a subset of all users. A model of a multicast system comprises a selected group of users, defined by the user's group membership. The group membership comprises users of subscriber stations subscribed to a particular multicast content. For brevity, the term “member subscriber station” is used to mean “user on a subscriber station” unless stated otherwise.
In one such a model the member subscriber stations are provided information with a certain content, e.g., news, movies, sports events and the like by one or more content servers via an assess network. The term access network is used herein to mean a collection of base stations and one or more base stations' controllers. Each member subscriber station monitors a forward link channel, over which the information is conveyed. The forward link channel may be shared among the member subscriber stations or may be established between each member subscriber station and the access network's station, e.g., a base station serving the member subscriber station. Because the content server fixedly determines the content, the member subscriber stations are generally not communicating back to the access network.
Alternatively, the source of information is a user, a member of the selected group; the user providing information intended for the remaining members of the selected group. If the user wishes to provide information, the user notifies the communication system, e.g., by pressing a push-to-talk (PTT) button. Typically, the user provided information is routed from the subscriber station to a base station on a dedicated reverse link. The base station then conveys the user provided information over a multicast forward link. As in case of the point-to-point communication system, the multicast communication system allows both landline and wireless subscriber station to access the system. The above-described service is also referred to as a group service. Examples of group service communication systems include dispatch services, such as local police radio systems, taxicab dispatch systems, Federal Bureau of Intelligence and Secret Service operations, and general military communication systems.
The above-mentioned multicast service communication systems are generally highly specialized purpose-build communication systems. With recent advancements in wireless cellular telephone systems there has been an interest in utilizing the existing infrastructure of the (mainly point-to-point) cellular telephone systems for multicast services. (As used herein, the term “cellular” systems encompasses both cellular and PCS frequencies.)
Introduction of a multicast services to cellular telephone systems requires integration of multicast services with the point-to-point services provided by the current cellular telephone systems. Specifically, both the access network and the subscriber station need to be able support functions allowing both the multicast mode and point-to-point communication mode. Because the point-to-point cellular telephone systems do not support multicast services, there is a need in the art for a method and a system for a multicast service procedures, specifically a multicast service initiation.